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#1 2015-10-20 07:59:03

technolog
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From: Europe / Slovenia / Grosuplje
Registered: 2012-01-28
Posts: 117

Where did 47MB of ram go?

I have two 4GB memory sticks installed.

When I run free -m, I get that some of that is missing:

              total        used        free      shared  buff/cache   available
Mem:           7953        1946        5287          25         720        5904
Swap:         12246           0       12246

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#2 2015-10-20 08:28:13

graysky
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Re: Where did 47MB of ram go?

Shared mem for video?


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#3 2015-10-20 08:44:08

technolog
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From: Europe / Slovenia / Grosuplje
Registered: 2012-01-28
Posts: 117

Re: Where did 47MB of ram go?

This is core2duo, it doesn't have integrated graphic card. The graphic card is Mobility Radeon HD 4330, with dedicated 512MB of ram.

p.s.: Thanks for the profile-cleaner. I use it often smile

Last edited by technolog (2015-10-20 08:50:27)

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#4 2015-10-20 08:50:04

graysky
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Re: Where did 47MB of ram go?

Something in th bios is likely reserving it would be my guess.


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#5 2015-10-20 08:51:33

technolog
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From: Europe / Slovenia / Grosuplje
Registered: 2012-01-28
Posts: 117

Re: Where did 47MB of ram go?

Great guess, but why so much?

[    0.000000] e820: BIOS-provided physical RAM map:
[    0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
[    0.000000] BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000000ef000-0x00000000000fffff] reserved
[    0.000000] BIOS-e820: [mem 0x0000000000100000-0x00000000b8f3ffff] usable
[    0.000000] BIOS-e820: [mem 0x00000000b8f40000-0x00000000b8f41fff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000b8f42000-0x00000000b9d6ffff] usable
[    0.000000] BIOS-e820: [mem 0x00000000b9d70000-0x00000000b9d7ffff] ACPI NVS
[    0.000000] BIOS-e820: [mem 0x00000000b9d80000-0x00000000bc4e0fff] usable
[    0.000000] BIOS-e820: [mem 0x00000000bc4e1000-0x00000000bc6e0fff] ACPI NVS
[    0.000000] BIOS-e820: [mem 0x00000000bc6e1000-0x00000000bde91fff] usable
[    0.000000] BIOS-e820: [mem 0x00000000bde92000-0x00000000bde99fff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000bde9a000-0x00000000bdebefff] usable
[    0.000000] BIOS-e820: [mem 0x00000000bdebf000-0x00000000bdecefff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000bdecf000-0x00000000bdfcefff] ACPI NVS
[    0.000000] BIOS-e820: [mem 0x00000000bdfcf000-0x00000000bdffefff] ACPI data
[    0.000000] BIOS-e820: [mem 0x00000000bdfff000-0x00000000bdffffff] usable
[    0.000000] BIOS-e820: [mem 0x00000000be000000-0x00000000bfffffff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000e0000000-0x00000000efffffff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000fec00000-0x00000000fec00fff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000fed10000-0x00000000fed13fff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000fed18000-0x00000000fed19fff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000fed1c000-0x00000000fed1ffff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000fee00000-0x00000000fee00fff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000ffe00000-0x00000000ffffffff] reserved
[    0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000023fffffff] usable

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#6 2015-10-20 09:24:56

Awebb
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Registered: 2010-05-06
Posts: 5,261

Re: Where did 47MB of ram go?

Give us brand and model of your mainboard and ask the vendor support the same question, while you're at it.

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#7 2015-10-20 09:44:22

R00KIE
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From: Between a computer and a chair
Registered: 2008-09-14
Posts: 4,734

Re: Where did 47MB of ram go?

You have to look at the whole dmesg output, there might be a clue somewhere. In my laptop I get something like this:

AGP: Checking aperture...
AGP: No AGP bridge found
AGP: Node 0: aperture [bus addr 0xb4000000-0xb5ffffff] (32MB)
Aperture pointing to e820 RAM. Ignoring.
AGP: Your BIOS doesn't leave an aperture memory hole
AGP: Please enable the IOMMU option in the BIOS setup
AGP: This costs you 64MB of RAM
AGP: Mapping aperture over RAM [mem 0xb4000000-0xb7ffffff] (65536KB)

This being a laptop there are no IOMMU options in the bios so I just live with it. In your case it might be something similar, or the kernel might be reserving those 47MB for some reason, on the other hand I'd say you shouldn't lose sleep because of 47MB out of 8GB wink


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#8 2015-10-20 09:46:38

technolog
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From: Europe / Slovenia / Grosuplje
Registered: 2012-01-28
Posts: 117

Re: Where did 47MB of ram go?

It is actually closer to 200MB:

~  cat /proc/meminfo | grep MemTotal
MemTotal:        8144512 kB

Model:

    product: HP ProBook 4510s (VQ740EA#BED)
    vendor: Hewlett-Packard
    version: F.18

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#9 2015-10-20 10:17:17

byte
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From: Düsseldorf (DE)
Registered: 2006-05-01
Posts: 2,046

Re: Where did 47MB of ram go?

I can't answer your question but here are some numbers for my systems (all 64-bit):

Core2Duo, 8 GiB: ~200 MiB missing
Haswell Xeon, 16 GiB: ~380 MiB missing
Athlon X2 7750, 4 GiB: ~160 MiB missing (includes 32 for onboard GPU)


1000

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#10 2015-10-20 12:22:53

R00KIE
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Re: Where did 47MB of ram go?

In my laptop running 64bit Arch:
Turion 64 X2 TL-64, 4GiB, ~139MiB missing


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#11 2015-10-20 19:02:44

graysky
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Re: Where did 47MB of ram go?

I have 4x8GB on my workstation.... seems to be missing 817 MB:

% free -m
              total        used        free      shared  buff/cache   available
Mem:          31951        1202       29988         249         759       30390
Swap:             0           0           0

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#12 2015-10-21 23:07:59

irrlicht
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Registered: 2010-12-06
Posts: 104

Re: Where did 47MB of ram go?

Maybe this output provide some idea for further investigation:


......
[    0.000000]   DMA zone: 21 pages reserved
[    0.000000] Memory: 16330228K/16677996K available (5592K kernel code, 922K rwdata, 1764K rodata, 1180K init, 1152K bss, 347768K reserved, 0K cma-reserved)
[    0.118673] PCI: MMCONFIG at [mem 0xf8000000-0xfbffffff] reserved in E820
[    0.170559] system 00:00: [mem 0xfed40000-0xfed44fff] has been reserved
....

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#13 2015-10-21 23:13:31

Trilby
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Re: Where did 47MB of ram go?

free -m displays memory in mebibytes or gibibytes .  Most hardware manufacturers report in megabytes or gigabytes.  Use `free -b` and you'll see it's all there.


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#14 2015-10-22 00:15:59

graysky
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Re: Where did 47MB of ram go?

% free -b
              total        used        free      shared  buff/cache   available
Mem:    33503375360  1092927488 28635348992   566378496  3775098880 31702773760
Swap:             0           0           0

34,359,738,368

Still missing 856,363,008.

Last edited by graysky (2015-10-22 00:16:17)


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#15 2015-10-22 06:53:20

mich41
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Registered: 2012-06-22
Posts: 796

Re: Where did 47MB of ram go?

Trilby wrote:

free -m displays memory in mebibytes or gibibytes .  Most hardware manufacturers report in megabytes or gigabytes.  Use `free -b` and you'll see it's all there.

RAM is never cheated like that, only storage.

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#16 2015-10-22 20:40:40

mpan
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Registered: 2012-08-01
Posts: 494
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Re: Where did 47MB of ram go?

~140MiB out of 4GiB reserved here.

technolog:
Remember that chipset itself needs memory, as well as all the controllers and devices installed on the mobo. Not only integrated video cards use RAM. Unfortunely you can't easily get information on what exactly uses which range. Disabling unused features may help a bit, but don't expect a miracle — especially with so low footprint (45MiB is really not a tragedy for a modern computer).

Also some motherboards, like older models of Gigabyte, may also use your HDD. To make it worse they don't care about the contents. The issue was fixed in later models and the "feature" may be disabled in BIOS setup.

mich41:
Don't use word "cheat" — it suggests someone is deceiving someone else, which is not the case here. Megabyte is and always was 1 000 000 bytes, and gigabyte is 1 000 000 000 bytes. Not 1 048 576 and 1 073 741 824. HDD manufacturers are using the units perfectly right. RAM vendors are ones who started to use it wrong: because they have to align sizes to powers of 2 and since the capacities were close to their SI counterparts, they started to use MB and GB to mean what we nowadays call MiB and GiB. Once planted the idea spread through industry and became a widely accepted notation, but the truth is that it's mass storage producers that are right in this case.

Last edited by mpan (2015-10-22 20:42:32)


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#17 2015-10-22 21:19:24

Xaero252
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Registered: 2011-11-28
Posts: 107

Re: Where did 47MB of ram go?

Similar to the above here:
12280MiB of ram (12G)
12011 of memory available according to free -m

running `dmesg | grep Memory:` you can see this line:

Memory: 12293748K/12573812K available (5626K kernel code, 886K rwdata, 1724K rodata, 1172K init, 1152K bss, 280064K reserved, 0K cma-reserved)

Using those numbers you'll find I am missing "280064" which, non-coincidentally is the amount of hardware reserved memory in the above line. You'll note there is a small discrepancy in these numbers:
Doing the math, the total memory according to that line is "12279.11328125Mib" which is just shy of 12280. I'm not entirely sure where this memory is mapped, but I'd imagine its mapped to the memory controller in the processor, and/or the BIOS and it's ACPI features. It's less than 1MiB so I'm not horribly worried.

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#18 2015-10-22 21:31:20

ewaller
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From: Pasadena, CA
Registered: 2009-07-13
Posts: 16,557

Re: Where did 47MB of ram go?

mpan wrote:

Megabyte is and always was 1 000 000 bytes, and gigabyte is 1 000 000 000 bytes. Not 1 048 576 and 1 073 741 824. .

I would say there are some who would disagree http://dictionary.reference.com/browse/megabyte

Count me as one who regards 1 MB as 2^20, not 10^6.   Sorry.
How many bytes in a kilobyte?  Here is an example from an obscure company in 1977 that shows the kbyte meant 1024 as far back as 1977.
https://archive.org/stream/byte-magazin … 3/mode/2up

Edit:  And as to disk storage...   A 1982 brochure for DEC RA-60/80 disk drives.  Run the numbers on page 36 for the RA-80.  Run the numbers on bytes/sector,  Sectors/track, tracks/cylinder and  cylinders/disk (take the product of all 4)  Compare that number (in bytes) and compare it to the published capacity of 121MB

I guess I just screwed my argument
https://archive.org/stream/bitsavers_de … 9/mode/2up

Last edited by ewaller (2015-10-22 22:21:21)


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#19 2015-10-22 22:29:18

mpan
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Posts: 494
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Re: Where did 47MB of ram go?

Xaero252:
Maybe the 1MiB is the conventional memory (640KiB). Possibly with upper memory region (384KiB). Dunno if Linux still maintains these, but the size would match.

ewaller:
Metric prefices are attested since at least 18th century. "Mega-" itself can be traced back to 19th century. All long before computers came into play and even predating SI units with which they're usually associated. "Mega-" and "giga-" mean, respectively, exactly 1000² and 1000³. I have never said if it were memory or mass storage vendors that started using it first — I'm just telling which are right. Both of them came after the prefixes were in use for nearly two centuries and they have just reused the words. Mass storage manufactures are using the original meaning, folks from memory — invalid, but close enough one.

The dictionary is not a source in this case, as it does not define anything. Dictionaries are just keeping observations on word set in use. What the link says is "megabyte is currently commonly used to denote 2²⁰ bytes". I have never tried to deny this.

I don't know what do you mean by that brochure. It's exactly right: 512 · 31 · 14 · 546 = 121 325 568 ≈ 121 · 1000² = 121MB.

Note: I'm myself used to thinking about megabyte as 1024², but I'm referring directly to mich41's use of word "cheat". It's a common accusation towards HDD producers, which is simply invalid.


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#20 2015-10-22 22:48:34

ewaller
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From: Pasadena, CA
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Posts: 16,557

Re: Where did 47MB of ram go?

As I indicated -- I  gave a counterargument to my own argument by finding an old ad that agrees with you.  I just don't regard it as being settled and always having been that way.

Anyway, lets drop it lest we hijack the thread further

Last edited by ewaller (2015-10-22 22:51:03)


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#21 2015-10-22 22:58:59

R00KIE
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From: Between a computer and a chair
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Re: Where did 47MB of ram go?

Count me in as someone who believes we should use powers of 2 for everything when dealing with computers, although I'd have to agree that we are be subverting the meaning of the SI prefixes.

Now for my argument: everything else in a computer works with powers of 2, the storage capacity is the odd one out. We all know that the smallest allocation unit in a disk is a sector, which is 512 bytes, this value is a power of 2. The closest you can have to 1000 bytes with whole allocation units is 1024, which again is a power of 2. You could say that things are like this for historic reasons but even today's SSDs use allocation units that are powers of 2.

It can be said that it is much easier to do the math with powers of 10, and I agree, but I suspect that the reason why storage manufacturers insist so much on using powers of 10 is because it is damn well convenient for them, as it inflates the number they can put on the sticker. If we take the logic to the limit, it would mean they could sell a disk with 1.953 512 byte sectors and still be able to call it a 1KB disk.

[1] https://support.microsoft.com/en-us/kb/121839


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#22 2015-10-23 00:53:53

mpan
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Re: Where did 47MB of ram go?

I agree with ewaller, sorry for the hijacking. A separate thread has been created for the issue.


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#23 2015-10-23 08:38:27

Awebb
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Registered: 2010-05-06
Posts: 5,261

Re: Where did 47MB of ram go?

How is this effect called today? Back in the day, we knew this as AGP Apperture size. It was memory reserved for anything AGP bus related. Isn't there a single EE working for a mainbord manufacturer here?

Last edited by Awebb (2015-10-23 08:38:55)

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#24 2015-10-23 09:31:03

mpan
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Registered: 2012-08-01
Posts: 494
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Re: Where did 47MB of ram go?

AGP aperture is one example, but RAM may be reserved for any device/purpose. You know… the integrated audio or network cards do not have their own CPUs or RAMs — they use the main ones. This is what makes the price difference between integrated and dedicated hardware.


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#25 2015-10-23 21:21:25

mich41
Member
Registered: 2012-06-22
Posts: 796

Re: Where did 47MB of ram go?

Most of this missing RAM seems to be eaten by Linux. Quite possibly the mem_map (which AFAIK uses about 1/64 of all RAM), kernel page tables and some other early allocated stuff isn't counted as "available memory" because it isn't available by the time this message is printed.

As for the BIOS, on my machine only about 3MB isn't "usable" and on OP's it seems to be 35MB. 3MB sounds reasonable, but I don't know where these 30 megs go, maybe for the shiny UEFI or Intel Management Engine?

mpan wrote:

You know… the integrated audio or network cards do not have their own CPUs or RAMs — they use the main ones. This is what makes the price difference between integrated and dedicated hardware.

Actually, they don't. I wouldn't count on recovering any memory by disabling this stuff.

Last edited by mich41 (2015-10-23 21:24:57)

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